Template for positioning interbody fusion devices

ABSTRACT

A template assembly is provided for marking locations on the disc annulus for the implantation of an interbody fusion device or the introduction of a working instrument. The template assembly includes a tubular body sized for percutaneous introduction into a patient and advancement to an affected intervertebral disc. An elongated shaft slidably extends through the tubular body and is threadedly engaged to the tubular body at its proximal end so that rotation of the shaft relative to the tubular body advances the shaft through the body. A guide foot is pivotably connected to the distal end of the tubular body to be pivoted from a first position aligned with the tubular body to a second deployed position oriented substantially perpendicular to the tubular body. The guide body is pivoted from the first position to the second position by advancement of the elongated shaft through the tubular body. The guide body in one embodiment defines a bore through which the working tip of an electrocautery instrument extends to mark the disc annulus. In another embodiment, the guide body itself defines an electrocautery projection. The template assembly can be anchored to the affected disc by a guide wire extending through the tubular body and about which the template assembly can be rotated to make an additional mark on the annulus at a predetermined distance from the first mark.

The present invention relates to a template to facilitate properpositioning of an implant into the intradiscal space between adjacentvertebrae. The template of this invention is particularly useful inconnection with interbody fusion devices, especially of the type shownand described in pending application Ser. No. 08/411,017, filed on Mar.27, 1995, owned by the assignee of the present invention and namingcommon inventors.

One of the most common sources of low back pain is damage or defects inthe spinal disc separating adjacent vertebrae. The disc can be herniatedor suffering from a variety of degenerative conditions, so that ineither case the anatomical function of the spinal disc is disrupted. Inrecent years the most prevalent treatment for these types of conditionshas been to fuse the two adjacent vertebrae together, therebyeliminating the normal movement of the affected disc. Depending upon thecondition of the disc, the entire disc may be removed, or the discannulus can be left intact with some or all of the disc nucleus removed.

With the removal of the disc or disc nucleus, something is required inthe intradiscal space to maintain the normal anatomic position of theadjacent vertebrae, at least until fusion occurs. One common device formaintaining the disc space is the interbody fusion device. In one typeof interbody fusion device, multiple such implants are disposed betweenthe adjacent vertebrae, separated by space to receive bone graftmaterial. An example of one such device is found in the above-mentionedco-pending application, Ser. No. 08/411,017, entitled INTERBODY FUSIONDEVICE AND METHOD FOR RESTORATION OF NORMAL SPINAL ANATOMY, filed onMar. 27, 1995, which disclosure and figures are incorporated byreference. Bilateral placement of two such fusion devices is depicted inFIGS. 1 and 2. The device 10 is tapered to maintain the normal curvatureof the vertebral level (L4-L5), and is threaded for engagement with thevertebral endplates E. The device 10 can be implanted through portalsformed in the disc annulus D. As illustrated in FIGS. 1 and 2, twofusion devices 10 are implanted to fill the disc space, effectivelymaintain the spinal curvature and provide adequate space between theimplants to be filled with bone graft material.

In the operative procedure for implanting the fusion device, a midlineincision is made to expose the anterior aspect of the vertebral bodiesat least one level above and below the affected motion segment. The softtissues are denuded at the target disc to provide adequate space toimplant the fusion device. Placement and positioning of the fusiondevice is typically assessed under direct vision, and the depth ofinsertion of the device assessed through lateral x-ray.

One difficulty with current techniques for implanting multiple implantsarises in determining the proper position for the implants to avoidinterference between the implants within the disc space and to maintainadequate spacing between the implants to receive bone graft material.There is a need for a simple device, or template, that can be easilyused by the spinal surgeon to determine the optimum position forimplanting a fusion device. In U.S. Pat. No. 4,772,287 to Dr. CharlesRay et al., a posterior technique is described in which holes aredrilled through each of the facet joints to provide a window forinsertion of prosthetic disc capsules. Although in this technique thewindows act as a guide for the insertion instruments, the size andorientation of these guide windows is severely limited by the facetjoint itself. For example, in the '287 Patent, the holes through thefacet joints are 11-mm, which is an appropriate size for the smallerimplant described in that patent. However, larger implants, such as thatdescribed in the above-mentioned co-pending application, cannot fitthrough the same small hole, and instead require complete removal of thefacet joint. Moreover, since the technique described in the '287 reliesupon the facet joint as a guide, it cannot be implemented in an anteriorapproach. Thus, the surgical approach described in this Ray patentcannot be used to implant the anterior fusion devices disclosed in theabove-mentioned co-pending application Ser. No. 08/411,017.

Another approach as described in U.S. Pat. No. 3,964,480, to Froning, isto use a stereotactic fixture to align instruments puncturing the discannulus. The '480 Patent describes the use of this fixture to provideunobstructed puncture of the intervertebral disc for injection offluids, such as radiographic contrast fluids and decompression drugs,such as chymopapain. However, as is evident from the figures of the '480Patent, the described stereotactic fixture is large and unwieldy, andcertainly does not lend itself well as a simple device for determiningthe position for implantation of a fusion device. In addition, thestereotactic fixture in the '480 patent is not suited for approachingthe disc space anteriorly.

The need of spinal surgeons for a device for positioning of multipleimplants within the intervertebral space is not adequately met by any ofthese prior devices or techniques. This need is magnified when suchimplants are placed via trocars and video-assisted spinal surgerymethods, where exposure of the disc space is more difficult and accuratesurgical orientation more critical. What is needed is a simple andeasily used template that allows a surgeon to readily locate where animplant should be inserted into the intradiscal space.

SUMMARY OF THE INVENTION

This unresolved need is met by the template assembly of the presentinvention. In one embodiment, the template assembly comprises a tubularbody sized for percutaneous introduction into the human body, andparticularly for introduction to the disc annulus. The tubular body hasa proximal end residing outside the patient and a distal end residingadjacent the disc annulus when the template is in use. The templateassembly further comprises an elongated guide foot pivotably connectedto the distal end of the tubular body by a hinge. The guide footinitially assumes a first retracted position in which the foot isaligned with the longitudinal axis of the tubular body to facilitateintroduction of the template via a seal or working channel anchored tothe skin. The guide foot is pivotable to a second deployed position inwhich the foot is oriented at an angle relative to the longitudinal axisof the tubular body. In this position, the guide foot can rest againstthe disc annulus.

The template assembly includes an elongated deployment shaft sized toslidably extend through the tubular body to project beyond the distalend of the body. The deployment shaft has a generally rounded or bluntdistal tip to bear against the guide foot as the shaft is pushed throughthe tubular body. In particular, as the shaft is advanced through thebody, the rounded tip pushes against the guide foot to cause the foot topivot about the hinge from the guide foot's first position to its seconddeployed position. To ensure a controlled deployment of the guide foot,the elongated shaft is threadedly engaged to the tubular body so thatrotation of the shaft relative to the tubular body achieves controlledadvancement of the shaft through the body. A handle at the proximal endof the deployment shaft provides adequate purchase for the surgeon torotate the shaft.

In one embodiment of the inventive template assembly, the guide footincludes a guide bore extending therethrough. The guide bore is sized toreceive the operative end of a marking instrument, such as the workingtip of an electrocautery device. In use, the template assembly isinitially introduced, preferably percutaneously, into the spinal spaceat the affected vertebral level. During initial introduction, thedeployment shaft is retracted into the tubular body and the guide footis oriented in its first position aligned with the longitudinal axis ofthe body, thereby presenting the smallest profile possible. When thedistal end of the tubular body is near the disc annulus, the deploymentshaft is advanced through the tubular body to gradually push the guidefoot to its pivoted second position.

With the guide foot in its deployed position, the elongated shaft can beremoved from the tubular body to permit introduction of a guide wirethrough the body. The guide wire is used to puncture the disc annulusand provide an anchor and a pivot point for the template assembly. Withthe guide wire firmly engaged in the spinal disc the guide foot is movedinto contact with the disc annulus. An electrocautery instrument is thenintroduced with its tip extending through the guide bore in the foot.The energized tip cauterizes the disc annulus, thereby marking theproper position for insertion of an interbody fusion device. Thetemplate assembly is then pivoted about the anchored guide wire so thatthe guide foot is positioned at the opposite side of the disc annulus. Asecond mark is made with the electrocautery instrument through the guidebore to denote the position for insertion of a second fusion device. Theguide wire and template assembly can then be removed. As the templateassembly is removed, the tissue surrounding the surgical site will pushagainst the guide foot causing it to pivot back to its first positionaligned with the tubular body.

In a second embodiment, the guide foot does not include a guide bore,but instead includes a feature for itself marking the disc annulus. Theguide foot can include a projection from the surface facing the discthat serves as an electrocautery tip. The template assembly includes anelectrical connection for providing electrical energy to the projectionof the guide foot.

One object of the present invention is to provide a template tofacilitate accurate positioning of implants within the intradiscalspace. A further object resides in features of the invention that permitpercutaneous introduction and use of the template assembly. Yet anotherobject is to provide a template assembly that can be easily used to markthe disc annulus, and that can be easily and quickly removed afterwards.

One important benefit of the template assembly of the present inventionis that it provides the surgeon with an accurate mark for positioningmultiple implants within the intradiscal space. Another benefit is thatthe template assembly can be readily adapted to accommodate differentsizes of implants and readily oriented to mark different locationsaround the disc annulus.

Other objects and benefits of the inventive template assembly willbecome apparent upon consideration of the following description of theinvention and the accompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 is an elevational view of the anterior aspect of the L4-L5 motionsegment shown instrumented with a pair of interbody fusion devices.

FIG. 2 is a side elevational view of the motion segment and fusiondevice construct depicted in FIG. 1.

FIG. 3 is an exploded view of the components of the template assemblyaccording to one embodiment of the present invention.

FIG. 4 is an enlarged partial cross-sectional view of the distal tip ofthe template assembly illustrated in FIG. 3, shown with the guide footin its initial insertion position.

FIG. 5 is an enlarged partial cross-sectional view of the distal tip asillustrated in FIG. 4, shown with the guide foot in its second deployedposition.

FIG. 6 is a partial top elevational view of the distal tip of thetemplate assembly as illustrated in FIG. 4.

FIG. 7 is a side cross-sectional view of the guide foot.

FIG. 8 is an end elevational view of the proximal end of the guide foot.

FIG. 9 is a side elevational view of the guide foot.

FIG. 10 is an end elevational view of the distal end of the guide foot.

FIGS. 11a-11b are pictorial representations of the template assemblypercutaneously inserted into the patient.

FIGS. 12a-12b are pictorial representations of the template assembly asthe guide foot is being deployed.

FIGS. 13a-13b are pictorial representations of the template assemblywith the guide foot fully deployed.

FIG. 14 is an enlarged pictorial representation of the template assemblyanchored to the disc and showing the use of an electrocautery instrumentin connection with the deployed guide foot for marking the disc annulus.

FIG. 15 is a side elevational view of another embodiment of the templateassembly in which the guide foot carries an electrocautery projectionfor marking the disc annulus.

FIG. 16 is an enlarged pictorial representation of a template assemblyanchored to the disc showing an alternative embodiment of the deploymentshaft and guide wire.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of promoting an understanding of the principles of thepresent invention, reference will be made to the embodiments illustratedin the accompanying drawings and specific language will be used todescribe the same. It is understood that the specific language andfigures are not intended to limit the scope of the invention only to theillustrated embodiment. It is also understood that alterations ormodifications to the invention or further application of the principlesof the invention are contemplated as would occur to persons of ordinaryskill in the art to which the invention relates.

Referring now to FIG. 3, a template assembly 15 in accordance with apreferred embodiment of the invention is illustrated. The templateassembly 15 includes an outer tubular body 17, an inner deployment shaft19 and a guide foot 21. The tubular body 17 is elongated along alongitudinal axis L between its proximal end 22 and its distal end 23.In use, the proximal end 22 is disposed outside the skin of the patientwhile the distal end 23 is situated adjacent the disc annulus of theaffected motion segment.

The tubular body 17 defines a central bore 24 from end to end toslidably receive the deployment shaft 19. At the proximal portion 27 ofthe tubular body 17, the central bore 24 includes a threaded bore 26.The proximal portion 27 is larger than the distal portion 29 of thetubular body 17, primarily to provide a smaller profile in the region ofthe vertebrae. In addition, the larger diameter of the proximal portion27 provides a better grip for the spinal surgeon manipulating thetemplate assembly 15 in situ. The deployment shaft 19 includes anelongated probe 30 configured to project beyond the distal end 23 of thetubular body 17 and having a generally rounded or blunt tip 31 forreasons set forth below. At the proximal end of the deployment shaft 19is a threaded portion 32 having threads that mate with the threaded bore26 of the tubular body 17. The proximal end of the deployment shaft isconfigured into a handle or knob 34 adapted to facilitate rotation ofthe deployment shaft 19 within the tubular body 17. The knob 34 ispreferably circular with knurling or other gripping feature defined onthe circumference of the knob to facilitate manual rotation of the knob.

Details of the guide foot 21 and its connection to the tubular body 17can be discerned from FIGS. 7-10. In particular, the guide foot 21includes a hinge portion 38 and a guide portion 45, with the portionspreferably oriented at right angles so that the guide foot takes on theshape of an "L", as seen in FIG. 7. The hinge portion 38 of the guidefoot defines a hinge boss 39 that is disposed between a pair of hingeflanges 28 projecting from the distal end 23 of the tubular body 17, asbest seen in FIGS. 4 and 6. A hinge pin 42 passes through bores in thehinge flanges 28 and a hinge bore 40 defined in the hinge boss 39 of theguide foot.

The hinge portion 38 of the guide foot 21 defines a proximal face 43that is closely adjacent the distal end 23 of the tubular body when theguide foot is in its first retracted position shown in FIGS. 3-4. Inthis first position the axis A of the guide portion 45 of the guide footis aligned with the longitudinal axis L of the tubular body. The guidefoot 21, and particularly the hinge portion 38, is circular in profile,as depicted in FIG. 8, with an effective outer diameter substantiallyequal to or less than the outer diameter of the tubular body 17. Thus,the guide foot 21 presents a profile that is no larger than the tubularbody, which is a beneficial feature for percutaneous introduction of thetemplate assembly 15. The guide portion 45 of the guide foot alsoincludes a tapered tip 46 at its distal end 44 to reduce the risk oftrauma to the tissue at the surgical site during introduction of thetemplate assembly.

As can be seen in FIGS. 3-5 the guide foot 21 is pivotably connected tothe tubular body 17 at the hinge 37. The hinge 37 is offset to one sideof the tubular body to take advantage of the "L" shape of the guide foot21. The guide foot 21 initially assumes its first position, shown inFIGS. 3-4, in which the axis A of the guide portion 45 of the guide footis aligned with, and preferably parallel to, the longitudinal axis L ofthe tubular body 17. The guide foot 21 is pivotable to its seconddeployed position in which the axis A of the foot is at an angle,preferably perpendicular, to the longitudinal axis L, as shown in FIG.5. The guide foot 21 is pushed from the first position of FIG. 4 to itssecond position of FIG. 5 by the rounded tip 31 of the elongated probe30.

The guide portion 45 of the guide foot 21 includes a guide bore 48defined therethrough. The guide bore 48 is sized to receive the workingtip of a marking instrument. Preferably, the marking instrument is anelectrocautery instrument that cauterizes the disc annulus. The markinginstrument must be capable of leaving a mark on the annulus sufficientto be visually observed by the spinal surgeon. This mark will identifythe proper position for inserting an implant into the disc space.Typically, the annulus will be fenestrated at the mark in order toreceive an interbody fusion device, such as the device described above.

Steps in the use of the template assembly 15 are depicted in FIGS.11a-13b. In the first step, the patient's skin S is punctured to receivea sealed trocar 50. The trocar 50 optimally provides a working channelfor the template assembly 15, as well as for diskectomy instrumentation,fusion devices and insertion instrumentation to be used subsequently.One significant advantage achieved by the template assembly 15 accordingto this invention is that it is well suited for use in percutaneousendoscopic procedures. It has been found that diskectomies and evenfusions can be performed using minimally invasive techniques, withoutthe necessity of the more difficult and invasive surgical procedures ofthe past.

With the sealed trocar 50 anchored to the skin S, the template assembly15 is introduced with the guide foot 21 in its first position, asdepicted in FIG. 11b. The deployment shaft 19 is retracted within thetubular body 17 during this step so that the rounded tip 31 does notproject beyond the distal end 23 of the body. Once the guide foot 21contacts the disc annulus D the template assembly 15 is withdrawnslightly to allow the guide foot to be pushed and pivoted to its secondposition. The deployment shaft 19 is advanced through the tubular body17 by rotating the knob 34 in the direction R shown in FIG. 12a. As theknob 34 and deployment shaft 19 is rotated, the probe 30 bears againstthe proximal face 43 of the guide foot 21 to cause the foot to pivotabout the hinge 37. As the probe 30 moves farther beyond the distal end23 of the tubular body 17, the guide foot pivots progressively throughthe position shown in FIG. 12b to its second fully deployed positionshown in FIG. 13b.

With the guide foot 21 in its second position, the template assembly 15is advanced toward the disc until the bottom surface 49 of the foot isagainst the disc annulus D. The deployment shaft 19 can be removed andreplaced with a guide wire 55, as shown in FIG. 14. The guide wire has asharp tip to pierce the disc annulus D and may include means to limitand control advancement of the guide wire into the disc. The guide wireis advanced into the disc a sufficient distant to effectively anchor thetemplate assembly 15 in position with the guide foot 21 in contact withthe annulus D. An electrocautery instrument 60 is then introduced to thesurgical site so that the working tip 61 extends through the guide bore48 in the guide foot 21. The working tip 61 is energized to cauterizethe disc annulus D leaving a mark MR on the annulus. This mark MR isvisible to the surgeon to identify the proper location for insertion ofan implant into the disc space. With the guide wire 55 still anchored inthe disc, the entire template assembly 15 can be pivoted about the guidewire in the direction T shown in FIG. 14. The guide foot 21 is thenoriented on the left side of the guide wire, on the opposite side of thedisc from the first mark MR. A second mark ML can then be made on thedisc annulus D using the electrocautery instrument. Once all thenecessary marks are made on the disc annulus, the guide wire can bewithdrawn, followed by the template assembly 15. As the assembly iswithdrawn from the surgical site, the surrounding tissue bears againstthe guide foot 21 to cause it to pivot about the hinge 37 and return toits first low-profile position.

In an alternative embodiment, shown in FIG. 15, the guide foot 21' ismodified from the foot 21 shown in FIG. 14. Specifically, the guide bore48 is eliminated in favor of an electrocautery projection 25' formed inthe bottom surface 49' of the guide foot. An electrical attachment 31'provides electrical energy to the guide foot 21'. In this instance, theguide foot 21' is formed of an electrically conductive material and theprojection 25' is configured to emulate the working tip of anelectrocautery instrument. One benefit of this configuration is that itis not necessary to introduce a separate electrocautery instrument tothe surgical site.

The components of the template assembly 15 are sized for percutaneousintroduction to the disc. In one specific embodiment, the assembly hasan overall length of 12.5 in. (31.75 cm) from the proximal end 22 of thetubular body 17 to the distal end 44 of the guide foot 21 in itsretracted first position. The tubular body 17 has an outer diameter inthe specific embodiment of about 0.437 in. (1.11 cm) at the proximalportion 27 and of about 0.250 in. (1.74 cm) at the distal portion 29.The central bore 24 of the tubular body 17 has a diameter of 0.125 in.(0.87 cm), while the deployment shaft has a diameter of 0.120 in. (0.30cm) to be slidably disposed within the central bore. The mating threadsbetween the deployment shaft 19 and the tubular body 17 are preferably1/4-20 UNC-2B threads.

In one specific embodiment, the guide foot 21 has an effective outerdiameter of 0.250 in. (1.74 cm) and a length from proximal face 43 tothe distal end 44 of 0.541 in. (1.37 cm). The guide bore 48 has adiameter of 0.136 in. (0.35 cm) with its center being located 0.313 in.(0.80 cm) from the proximal face 43. The distance to the center of theguide bore 48 establishes the spacing between the two marks MR and MLmade on the disc annulus D to identify the location for insertion of thefusion implants. Referring again to FIG. 14, it can be seen that themark MR is made at predetermined distance from the guide wire 55anchored in the disc. When the template assembly is pivoted about theguide wire, the mark ML is separated from the mark MR by twice thatpredetermined distance. This distance between marks is determined by thenecessary separation between the interbody fusion devices to beintroduced into the intradiscal space. In the specific illustratedembodiment, the fusion devices may have a maximum diameter of about0.787 in. (2.00 cm), which requires the two marks MR and ML to be atleast that distance apart.

In the illustrated embodiments, the template assembly is configured tomark the location for insertion of two bilateral fusion devices in thelower lumbar spine. Naturally, the dimensions of the guide foot 21 andthe guide bore 48, or cauterizing projection 25', will be reduced inaccordance with the geometry of the spinal anatomy at the affectedmotion segment. In addition, the template assembly can be configured toprovide guide marks for the implantation of more than two fusiondevices. In procedures involving three or more such devices, thetemplate assembly can be oriented over successively made marks with theguide wire anchored into the disc at the marks. New marks can be made inthe described fashion by pivoting the template assembly about the guidewire. The distance to the center of the guide bore 48 or cauterizationprojection 25' would be reduced accordingly.

The invention has been illustrated and described in detail in theforegoing description and accompanying drawings, which are intended tobe illustrative but not restrictive in character. It is of courseunderstood that only the preferred embodiments have been shown and thatall changes and modifications that fall within the spirit of theinvention are desired and contemplated to be protected.

For example, the template assembly 16 has been described as used with aseparate guide wire 55 to anchor and orient the assembly during themarking steps. In the illustrated embodiments, the deployment shaft 19was required to be removed to accommodate the guide wire 55.Alternatively, the deployment shaft can be cannulated to receive theguide wire therethrough such as deployment shaft 19' depicted in FIG.16. In this embodiment, the deployment shaft need not be removed. Therounded tip 31 of the deployment shaft will not traumatize the discannulus. The diameter of the deployment shaft is sufficient to accept athin guide wire.

The guide foot 21 has been described and depicted as having an "L"shape. Other configurations are contemplated by this invention, providedthat the guide bore or cauterization projection can be maintained at thepredetermined distances discussed above. In accordance with the presentinvention, the components are contemplated to be formed from surgicalgrade stainless steel or other medically suitable material. The guidefoot can be composed of a plastic material to minimize heat conductionfrom the working tip of the electrocauterization instrument.Alternatively, the device may be fabricated of a radioluscent plastic orcomposite material to allow unimpeded viewing of the guide wireplacement and anatomical orientation. Other suitable materials for thecomponents of the template assembly 15 are contemplated.

While the invention has been described for use in positioning bilateralfusion devices, the same marking capability can be used for otherprocedures. For example, the template can be used to mark the locationfor insertion of various instruments and tools into the disc space.Other uses for the template assembly 15 of the present invention mayreadily present themselves to persons of ordinary skill in this art.

What is claimed is:
 1. A template assembly to facilitate the placementof an implant or instrument at a portion of the spine, such as the discspace between adjacent vertebrae comprising:a tubular body sized forintroduction into a patient for advancement to the portion of spine,said tubular body having a longitudinal axis, and a proximal enddisposed outside the patient and a distal end disposed adjacent theportion of the spine when said body is within the patient; an elongatedguide foot having an axis and defining an opening therethrough sized toreceive the implant or instrument extending therethrough, said guidefoot being pivotably connected to said tubular body at a hinge disposedat said distal end, whereby said guide foot is pivotable between a firstposition in which said axis of said foot is generally parallel to saidlongitudinal axis of said tubular body for introduction into thepatient, and a second position in which said axis is oriented at anangle relative to said longitudinal axis of said tubular body with saidopening oriented toward the portion of the spine; and deployment meansextending through said tubular body and operating on said guide foot forcausing said guide foot to pivot about said hinge between said firstposition and said second position.
 2. The template assembly according toclaim 1, wherein said deployment means includes an elongated shaft sizedto be slidably advanced through said tubular body beyond said distal endof said tubular body, said elongated shaft having a tip for bearingagainst said guide foot as said shaft is advanced through said tubularbody.
 3. The template assembly according to claim 2, wherein saidelongated shaft is threadedly engaged to said tubular body, whereby saidshaft is advanced through said tubular body by rotation of saidelongated shaft relative to said tubular body.
 4. The template assemblyaccording to claim 3, wherein said elongated shaft includes a knobdisposed outside said tubular body when said shaft is advanced throughsaid tubular body, said knob configured to permit manual rotation ofsaid shaft relative to said tubular body.
 5. The template assemblyaccording to claim 2, wherein said elongated shaft is cannulated.
 6. Thetemplate assembly according to claim 1, wherein;said tubular body iscylindrical and has an outer diameter; and said guide foot defines acircular profile perpendicular to said axis, said circular profilehaving an effective diameter substantially equal to or less than saidouter diameter of said tubular body.
 7. The template assembly accordingto claim 1, wherein said hinge includes:a boss defined in said guidefoot; a pair of flanges projecting from said distal end of said tubularbody, said flanges spaced apart to straddle said boss of said guidefoot; and a hinge pin extending through said boss and said pair offlanges to pivotably connect said guide foot to said tubular body. 8.The template assembly according to claim 7, wherein said tubular bodyhas an outside dimension and said flanges are disposed within saidoutside dimension.
 9. The template assembly according to claim 1,wherein said opening in said guide foot is a bore sized to receive aworking tip of an instrument adapted for creating a mark on the discannulus identifying a location on the annulus.
 10. A kit comprising atemplate assembly according to claim 9 and an electrocautery instrumenthaving a working tip sized to extend through said bore of said guidefoot of said template.
 11. A kit comprising a template assemblyaccording to claim 1, and a guide wire having a tapered tip forpenetrating the portion of the spine, said guide wire sized to slidablyextend through said tubular body and said tip configured to penetratethe portion of the spine to anchor the assembly to the portion of thespine, whereby said tubular body is rotatable about said guide wire whensaid guide wire is anchored in the portion of the spine.
 12. The kitaccording to claim 11, wherein said deployment means includes anelongated shaft sized to be slidably advanced through said tubular bodybeyond said distal end of said tubular body said elongated shaft havinga tip for bearing against said guide foot as said shaft is advancedthrough said tubular body.
 13. The kit according to claim 12, whereinsaid elongated shaft is cannulated to receive said guide wiretherethrough.
 14. The template assembly according to claim 1, whereinsaid guide foot is L-shaped with a hinge portion connected to saidtubular body and a guide portion oriented substantially perpendicularthereto with said guide portion defining said axis of said guide footand said opening.
 15. The template assembly according to claim 14,wherein said guide portion of said guide foot is tapered at an end ofsaid guide portion distal from said hinge portion to facilitateintroduction of said guide foot into the patient when said guide foot isin said first position.